LCodeGen::CallKnownFunction gets the function in register.

src/arm64/lithium-codegen-arm64.h

Index: src/arm64/lithium-codegen-arm64.h
diff --git a/src/arm64/lithium-codegen-arm64.h b/src/arm64/lithium-codegen-arm64.h
index a73bb8caaff618b1b0203075d8869485fecef6fc..08a699d0e52da5ab354262eacc01856d6a6981b9 100644
--- a/src/arm64/lithium-codegen-arm64.h
+++ b/src/arm64/lithium-codegen-arm64.h
@@ -318,15 +318,11 @@ class LCodeGen: public LCodeGenBase {
                                LInstruction* instr,
                                LOperand* context);
 
-  // Generate a direct call to a known function.
-  // If the function is already loaded into x1 by the caller, function_reg may
-  // be set to x1. Otherwise, it must be NoReg, and CallKnownFunction will
-  // automatically load it.
+  // Generate a direct call to a known function.  Expects the function
+  // to be in x1.
   void CallKnownFunction(Handle<JSFunction> function,
-                         int formal_parameter_count,
-                         int arity,
-                         LInstruction* instr,
-                         Register function_reg = NoReg);
+                         int formal_parameter_count, int arity,
+                         LInstruction* instr);
 
   // Support for recording safepoint and position information.
   void RecordAndWritePosition(int position) OVERRIDE;